METHOD OF MANUFACTURING SHELL FORMED CONSTRUCTIONS

Abstract: The present invention relates to a method of manufacturing shell-shaped constructions, preferably of concrete, such as houses, ships' hulls, etc. According to the invention two flexible sheaths are arranged, an upper sheath outside a lower sheath, with a space (3) between them (1, 4) into which powder material is filled. Both sheaths are attached to a support surface or to the ground (2), after which pressure medium such as air is blown in between the support surface/ground (2) and the lower sheath/membrane (1), so that the sheath/membrane construction is inflated to the desired shape (9), after which the space (3) between the sheaths/membranes is evacuated with the aid of a vacuum pump (6), and the powder is thereafter compacted to rigidity, after which concrete, such as fibre-reinforced concrete, is sprayed onto the exterior of the upper sheath/membrane (4) and when the concrete has set/solidified the pressure medium in the lower space (7) is released and air is allowed to enter the space (3).

Description: METHOD OF MANUFACTURING SHELL FORMED CONSTRUCTIONS Technical field: The present invention relates to a method of manufacturing shell-shaped constructions, preferably of concrete, such as houses, ships' hulls, etc. Background art: It is already known to coat an inflated rubber membrane with concrete either before or after inflation, the membrane being removed after the concrete has set. The known technology can be divided into three groups: 1. A flexible membrane (rubber) is coated with concrete, and suitably reinforcing mesh, after which the membrane is inflated to the desired size and the concrete then allowed to solidify (SE 330435). 2. A non-flexible membrane is inflated and concrete is then applied externally by means of spraying (SE 357230). 3. A flexible or non-flexible membrane is inflated and the "balloon" is then coated internally with an insulating foam which is allowed to solidify, thus improving the rigidity of the balloon, after which concrete is sprayed on internally (EP 0357151). The drawbacks of the above procedures are: 1. The method functions well for smallish constructions, e.g. a hemisphere with less than 5-6 m diameter. The procedure is difficult to perform satisfactorily with larger constructions due to problems of instability. Very moderate winds during the casting, for instance, may cause deformation of the "balloon" which jeopardizes the entire casting. 2. Here the problems of instability described under 1. are eliminated by the "balloon" being pumped up to a higher pressure, e.g. 0.1 bar, or about 10 times the pressure used under 1. The drawback with high pressures is the enormous forces required to keep the balloon/ hemisphere on the ground. (One ton per square metre is required for a pressure of 0.1 bar in the hemisphere, a construction with an area of 200 m 2 takes 200 ton.) 3. Here the instability problems are solved with the aid of foam and moderate pump pressure can be used. The drawback with this procedure is the complex internal reinforcing system required and the great waste of concrete which is unavoidable when spraying internally (from below). It is also known to fill powder into a space between two pipes (membranes) and evacuate the air from this space so the powder is compacted thereby producing a more rigid body (US 3258883). There is no intimation in this publication of using the procedure for building purposes. Summary of the invention: The invention constitutes a solution to the problems defined above and also offers additional advantages over current technology. The method according to the invention is characterized in that two flexible sheaths or membranes are arranged, an upper sheath outside a lower sheath, with a space between them into which powder material is filled, both sheaths being attached to a support surface or to the ground, after which pressure medium such as air is blown in between the support surface /ground, or an auxiliary membrane, and a lower sheath/ membrane, so that the sheath/ membrane construction is inflated to the desired shape, after which the space between the sheaths /membranes is evacuated with the aid of a vacuum pump, thereby compacting the powder to rigidity, after which concrete, such as fibre-reinforced concrete, is sprayed onto the exterior of the upper sheath/ membrane, and that when the concrete has set/ solidified the pressure medium is released and air is allowed to enter the space. It is thus possible to build normal-sized or large buildings of hemispherical shape, round or flattened, or shapes deviating from these, at relatively low cost. In an alternative embodiment pressure medium /air is blown in between a support surface or an auxiliary member and one of the sheaths placed beneath the support surface / auxiliary member, so that the sheath/ membrane construction is blown downwardly to the desired shape in a space provided for the purpose. This alternative is particularly suitable for ships' hulls, whereas the first alternative is suitable for building houses. Brief description of the drawings: The invention is illustrated in more detail in the accompany drawings in which Figures la-lc show various stages of erection of a mould onto which concrete will be sprayed, i.e. a first stage in constructing a house, a ship's hull, etc. Figure Id shows concrete being sprayed on and Figure le removal of the membrane. Figures 2a-2c show the inflation point at various stages of the erection. Figures 3a-3b show a detail of the method according to the invention. Figure 4 shows a substructure manufactured in accordance with the invention, and Figures 5a-5b alternative substructures manufactured in accordance with the invention. Figures 6a-6e show the alternative production of ships' hulls and the like. Preferred embodiment: Figure la reveals how two membranes, an upper membrane (4) and a lower membrane (1) are placed and anchored in a foundation (2). A powder material such as sand, sawdust, porous clay pellets, etc., is filled into the space (3) between the membranes. The membranes (1, 4) are attached to the foundation (2) or a support surface. Figure lb shows how a pressure medium such as air is blown in under the lower membrane (1) with the aid of a pump (5), and the membranes (1, 4) with the powder between them are lifted to the desired shape, possibly under partial vacuum. A positive pressure of 0.001-0.01 bar in the space (7) is sufficient, depending on the diameter of the membrane. However, the diameter should be relatively large (for constructing a house, for instance). When the desired shape has been obtained, the air is evacuated from the powder space (3), see Figure lc, the powder layer thereby being compacted so that satisfactory rigidity and strength are obtained. This rigidity prevents deformation of the parts of the mould and a firm template is obtained onto which concrete can be sprayed. Evacuation is obtained with the aid of a vacuum pump (6). The vacuum will cause the membranes (1, 4) to be pressed towards each other, thus compressing the powder. An extremely rigid composite is thus produced, giving good stability to the entire casting mould. (A packet of coffee, for instance, is hard and rigid as long as it is evacuated, but becomes limp after being punctured.) Figure Id shows the next step in which concrete and fibre, fibre-reinforced concrete, is sprayed (at 8) against the mould (9b). When the concrete has set the air is released from the space (7) below the membrane (1) and air is allowed into the space (3) between the membranes (1, 4). Compacting is thus cancelled and the membranes can be removed for re-use while the substructure (9a) remains. Lower vacuum may possibly be used during inflation when performing the method according to the invention, in order to prevent the powder from running. Concrete is sprayed on here (Figure Id), such as concrete and fibre, or sand and cement, water and fibre separately. Figure le shows how the air is released (11) from the space (3), whereupon the "concrete shell" (9a) remains and compacting disappears in the space (3). The membranes (1) and (4) can now be removed and a dome or hemisphere remains. The procedure also allows a certain modification of the shape after inflation, in that the powder material in the space (3) can be deposited in different thicknesses , or may consist of powder having different density. A more elliptical shape can be achieved, for instance, by using a powder with higher density (sand and sawdust) at the centre, while the remainder may be primarily sawdust. The membrane will be weighted down where the sand is and will not be blown up as high as otherwise. Figure 4 shows a flattened, elliptical shape obtained by placing heavier powder material at the centre. Figure 2a shows the vacuum connection (12) to the powder space (3), there being several located around the periphery, at the start of inflation. (13) is a mesh or strainer to prevent the powder from being withdrawn at the same time. (2) is a concrete slab and (15) is an attachment bolt, e.g. an expansion- shell anchor bolt. Figure 2b shows the same parts following inflation of the space (7), showing how the membranes (1 and 4) are attached to a support surface (20). Figure 2c shows the situation for the same parts when the air in the space (7) has been released and the partial vacuum in the space (3) has been cancelled. Figures 3a and 3b show superstructures on the substructure, e.g. a window, consisting of a shell (16) and a cover (17). These parts are fitted together, and the space formed is placed under partial vacuum so that the body becomes attached (by means of suction) to the surface below. This procedure can be used for all types of apertures, doors, windows, ventilation, etc., and concrete is sprayed on outside these protrusions in the same way as for the rest of the substructure. Figures 5a and 5b show alternative substructures in which the shape has been influenced during the inflation process with the aid of wires, bands, etc. (27). Conventional insulation may be applied outside the body (9a), and possibly also an impervious layer, after which another layer of concrete with fibres is sprayed on. The dome (9a) can be reinforced in conventional manner using steel rods, for instance, or cables, wires, etc. to take up the considerable tensile strain that may arise as a result of the design of the building, e.g. large apertures, or the choice of shape. Figure 6a-6b shows the production of a ship's hull in accordance with the invention. Figure 6a shows an example of membrane shape. Figure 6b is a section along the line A-A in Figure 6a. (18) is an auxiliary membrane and (1 and 4) are membranes as above. (5) is a pressure pump and (6) a vacuum pump. The procedure is in accordance with the first example. Main lines (19) to the outer membrane, see Figure 6c, in order to achieve the desired hull shape. Pressure medium (e.g. air) is pumped by a pressure pump (5) into a space between the auxiliary membrane (18) and the inner membrane (1), and the sheath/ membrane body is blown down into a space for the purpose below the construction. The space (3) is then placed under partial vacuum and the powder therein is compacted to rigidity (Figure 6d). When the compact mould has been obtained as above, the auxiliary membrane is removed (Figure 6e), and concrete + fibre material are sprayed on (at 21) to produce a ship's hull. After solidification the membrane can be removed when the partial vacuum in the space (3) has been cancelled. The method according to the invention can be varied in many ways within the scope of the following claims.

Claims: CLAIMS 1. A method of manufacturing shell-shaped constructions, preferably of concrete, such as houses, ships' hulls, etc., characterized in that two flexible sheaths are arranged, an upper sheath outside a lower sheath, with a space (3) between them (1, 4) into which powder material is filled, both sheaths (1, 4) being attached to a support surface or to the ground (2), after which pressure medium such as air is blown in between the support surface /ground (2) and the lower sheath/ membrane (1), so that the sheath/ membrane construction is inflated to the desired shape (9), after which the space (3) between the sheaths /membranes is evacuated with the aid of a vacuum pump (6), thereby compacting the powder to rigidity, after which concrete, such as fibre-reinforced concrete, is sprayed onto the exterior of the upper sheath/ membrane (4) and that when the concrete has set/ solidified the pressure medium in the lower space (7) is released and air is allowed to enter the space (3). 2. A method as claimed in claim 1, characterized in that before blowing in of the pressure medium has been completed, cables, wires or bands are placed over the upper membrane (4) so that the final product acquires a shape deviating from hemispherical or partially spherical shape. 3. A method as claimed in claim 1, characterized in that a superstructure such as a shell-shaped, nose-like element is applied outside the outer membrane (4), beside the membrane, after which the space inside this element is evacuated and the element thus becomes attached to the membrane (4), after which concrete is sprayed externally onto the outer membrane and the superstructure. 4. A method as claimed in claim 1, characterized in that pressure medium/ air is blown in between a support surface or an auxiliary member (18) and one of the sheaths (1) placed beneath the support surface /auxiliary member (18), so that the sheath/ membrane construction is blown downwardly to the desired shape in a space provided for the purpose. 5. A method as claimed in one or more of the preceding claims, characterized in that the powder in the space (3) is poured in with different density and /or different thickness at different parts of the surface so that the final product acquires a shape deviating from hemispherical or partially spherical shape. 6. A method as claimed in one or more of claims 1-5, characterized in that when the body has been fully cast, insulating material is placed thereon and then covered by plastic such as shrink plastic, after which concrete, such as fibre-reinforced concrete, is sprayed onto the plastic in an outer layer

Inventors: LARSSON HANS GUNNAR, LARSSON, HANS, GUNNAR
Applicants: H G TECH AB, LARSSON HANS GUNNAR, H.G.TECH AB, LARSSON, HANS, GUNNAR
Application year: 1994
Main classification: E04G11
IPC codes: E04G11